Method of making heat transfer tube

Abstract

A heat transfer tube comprising an inner tube formed of copper or steel, an intermediate layer having a uniform thickness, mounted on the outer periphery of the inner tube and formed of a low melting point metal such as solder, tin or lead and an outer tube of lead or lead alloy mounted on the intermediate layer on the inner tube and metallurgically bonded with the intermediate layer when the low melting point metal is melted.

What is claimed is: 
     
       1. A method of manufacturing a heat transfer tube, comprising the steps of: placing an intermediate metal layer having a low melting point around an inner tube formed of copper or steel;   heating the intermediate layer to a temperature above its melting point to metalurgically bond it to the inner tube; and   coating the molten intermediate layer with lead or a lead alloy while the intermediate layer is in a molten state to form an outer layer around the inner tube.   
     
     
       2. The method of claim 1, wherein the coating step is performed after heating of the intermediate layer is stopped. 
     
     
       3. The method of claim 2, wherein said step of heating the intermediate layer is performed by inserting a heater into the inner tube.